摘要:

The low‐velocity Barkas‐effect correction term for the Bethe–Bloch stopping‐power formula has been calculated with each of the three extant formalisms for targets with atomic numbers from 1 to 18 and for projectile velocities from 0.025cto 0.3c. Comparison of each with measurements on aluminum revealed which formalism provided the best fit over three different projectile velocity intervals. The method yielding the generally superior agreement was used to calculate the stopping power of each element (except Li, F, Na, Mg, P, and Cl) for protons and alpha particles with energies between 0.5 and 5.0 MeV. Results corresponded very closely to those of an existing fit to most known experimental data.

ISSN:0021-8979    

DOI:10.1063/1.345094

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The recombination and dissociation of H+2and H+3ions incident upon metal surfaces leads to H, H2(v‘), and H−products rebounding from the surface. A four‐step model for H+2‐ion recombination generates H2(v‘) via resonant electron capture through theb 3&Sgr;+uandX 1&Sgr;+gstates. A molecular trajectory analysis provides final‐state H2(v‘) distributions for incident energies of 1, 4, 10, and 20 eV. The calculated H2@B:H+2yields compare favorably with the observed yields. A similar four‐step model for incident H+3proceeds via resonant capture to form the H3(2p 2E’→2p 2A1) ground state, in turn dissociating into H+H2(v_‘), with the fragment molecule rebounding to give the final H2(v‘) distribution. Comparing the final populationsv‘≥5 for incident H+2or H+3shows that the H+3ion will be more useful than H+2for H−generation via dissociative attachment. Molecular ions incident upon low‐work‐function surfaces generate additional H2(v‘) via resonant electron capture through excited electronic states and provide two additional sources of H−production: Direct H−production by H dissociation products rebounding from the surface and H−production through the formation of H−2in the surface selvage that in turn dissociates into H+H−. The H−2in the selvage is formed by resonant capture to the low‐lying vibrational levels of H2(v‘), and complements dissociative attachment to high‐lying levels in the discharge. The H, H2(v‘), and H−yields are inventoried for H+3incident upon barium surfaces.

ISSN:0021-8979    

DOI:10.1063/1.345095

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Exact solution of the three‐dimensional linear equations of piezoelectromagnetism is obtained for doubly rotated piezoelectric crystal plates surrounded by vacuum and excited by face traction. A generalized Poynting’s theorem is derived for general media in which electromagnetic and mechanical fields interact with each other. For linear piezoelectric crystals it is shown that the generalized theorem may still be interpreted as an energy theorem, and hence densities of energy stored in the electric, magnetic, and elastic strain fields can be identified. Radiated power, per unit surface area and averaged over the period, and induced strain and electric fields in the middle plane of the plate are calculated for doubly rotated quartz plates whose cut orientations follow the upper and lower loci of zeros of the first‐order temperature coefficient of frequency of thex1‐thickness‐shear mode. Quality factors and partition of stored energies are also examined.

ISSN:0021-8979    

DOI:10.1063/1.345096

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Systems consisting of two‐dimensional semi‐infinite slabs in front of conducting or insulating planes are examined. The slabs which are symmetric may either be thick or thin and of rather general shape. Some of these systems may be identified with magnetic recording head systems, while others are complementary to systems examined by Sproston [IEE Proc.129, 619 (1982)] and Gibbings [J. Electrostat.6, 121 (1979)]. Four examples are treated giving the behavior of a dimensionless intensity over their geometrical surfaces. On the conducting plane of certain types of systems, it is seen that the intensity may be approximated quite well by that due to an ideal rectangular slab and also that it decreases along the plane faster than that due to the ideal slab.

ISSN:0021-8979    

DOI:10.1063/1.345097

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

We discuss the thermal and optical properties of the lyotropic liquid crystal decylammonium chloride/water/NH4Cl (DACl‐LLC) from −40 to 80 °C. Combined use of DACl‐LLC and highly tapered monomode optical fibers allows sensing of temperature (from room temperature up to 65 °C).

ISSN:0021-8979    

DOI:10.1063/1.345098

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Optical‐absorption calculations and finite‐element methods are used to calculate time‐dependent temperature profiles in two contrasting laser‐addressed liquid‐crystal displays. It is shown that the presence of conducting electrode layers has a significant effect on the temperature profiles both by affecting the optical‐absorption characteristics of the cell and the resulting thermal conductivity. It is shown that efficient optical absorption does not necessarily result in the best cell‐addressing performance.

ISSN:0021-8979    

DOI:10.1063/1.345099

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Measurements are reported of the second‐harmonic distortion in 1.3‐&mgr;m InGaAsP distributed feedback lasers operating at different temperatures. A minimum of the second‐harmonic distortion exists at a particular bias current when the laser is operating at low temperature (10 °C). The minimum shifts to a higher bias current when the operating temperature is raised. At an even higher temperature, the minimum dissappears. A temperature‐dependent model of the second‐harmonic distortion, based on an equivalent circuit analysis, is presented to explain the experimental results.

ISSN:0021-8979    

DOI:10.1063/1.345100

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

We have used the light‐induced grating erasure technique to measure the photorefractive properties of pure and iron doped BaTiO3. Our experiments were performed using an anisotropic configuration which forbids beam coupling and self‐diffraction between the writing beams, resulting in plane parallel intensity fringes that do not change with time. This allowed direct measurement of the charge transport processes without any feedback on the grating due to wave‐mixing processes. The results from these experiments show that the photorefractive parameters known as the trap densityNprand the mobility‐recombination time product &mgr;&tgr;r, vary with intensity and are not material constants.

ISSN:0021-8979    

DOI:10.1063/1.345101

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

This paper is concerned with transverse effects arising from diffraction in a nonlinear Fabry–Pe´rot filled with a self‐focusing medium. It is shown that the resulting bistable loop is ‘‘enhanced’’ with respect to the plane‐wave one. This result contrasts with the self‐defocusing case where optical bistability disappears when decreasing the width of the input beam.

ISSN:0021-8979    

DOI:10.1063/1.345102

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Surface acoustic waves for micrograting reflectors have been characterized. Based on the perturbation theory, eight different types of structures on an acoustic waveguide were analyzed. Results of simulations of all eight types of corrugation structures were evaluated in order to find the least leaky waveguide, the most efficient reflector (with minimum necessary perturbations), and the optimal mode shape for improved performances. General design curves are presented in order to illustrate the behavior of the incident and reflected waves under a variety of structural conditions. Analytic expressions for the calculations of the mode amplitude and mode shape, and for general acoustic corrugations are derived and then the simulations results are presented.

ISSN:0021-8979    

DOI:10.1063/1.345103

出版商:AIP    

年代:1990

数据来源: AIP